Hydrobromination of alpha-olefins

ABSTRACT

A method is provided for reducing the air-blowing time required to activate a substantially pure alpha-olefin for reaction with anhydrous hydrogen bromide to produce a primary alkyl bromide. The method involves admixing at least four weight percent of a previously activated alpha-olefin with the substantially pure alpha-olefin prior to air-blowing.

United States Patent I 1 1 7 Boyle et al. 1451 Oct. 17, 1972 54]HYDROBROMINATION OF ALPHA- 3,482,000 12/1969 Femald etal.....260/683.l5 1) OLEFINS Primary Examiner-Daniel D. Horwitz [72]Inventors John Boyle Moon Township Attorney-Meyer Neishloss, Deane E.Keith and legheny County; Clarence R.

Murphy, Allison Park; William L. c'caffney Walsh, Glenshaw, all of Pa.

[73] Assignee: Gulf Research 8: Development Company Pittsburgh timerequired to activate a substantially pure alpha- [22] Filed: Sept. 9,1969 olefin for reaction with anhydrous hydrogen bromide [211 pp No 260to produce a primary alkyl bromide. The method in- [5 7] ABSTRACT volvesadmixing at least four weight percent of a previously activatedalpha-olefin with the substantially 52 us. 01.; ..260/663 p p e prior toair-blowing- 511 Int. Cl ..-.C07c 17/08 I [58] Field of Search..260/663,683.1-5 DY [56] References Cited I y 9 claim,- 2 DrawingFigures UNITED STATES PATENTS 3,422,145 1/1969 Steinmetz ..260/663RECYCLE l8 A 10 20 pRo ucr ACTIVE 24 RECOVERY O L E FIN 14 v 22 GASCONTAINING H FREE MOLECULAR A method is provided for reducing theair-blowing PATENTEDnm 11 m2 3. 699 '.1 79

sum 1 m2 FIG. I

' RECYCLE l8 A 2 l6 TO PRODUCT ACTIVE 2o 24 RECOVERY OLEFIN GASCONTAINING HBr FREE MOLECULAR INVENTORS JOHN P BOYLE BY CLARENCE R.MURPHY WILLIAM L. WALSH minnow 11 m2 3.699.179

SHEEI 2 [IF 2 F IG 2 YINOPERATIVE REGION Y I 55' v A I m I 05 gOPERATIVE I REGION. 7 55 E :3 n- 2:

E5 INOPERATIVE REGION Q0. I 1 I- 60 80 IOO I I 200 TEMPERATURE CINVENTORS JOHN I? BOYLE BY CLARENCE R. MURPHY WILLIAM L. WALSHHYDROBROMINATION OF ALPHA-OLEFINS This invention relates to an improvedmethod for activating an alpha-olefin for reaction with anhydroushydrogen bromide to produce a primary alkyl bromide.

The addition of HBr to alpha-olefins to produce primary and secondarybromides is known. It is also known that primary alkyl bromides can bemade by the addition of I-IBr to alpha-olefins in the simultaneouspresence of free radical promoters, such as ultraviolet light (U.S. Pat.No. 2,307,522); extraneously added peroxides, such as organic peroxides(U.S. Pat. No. 2,058,466 and British Pat. No. 843,234); or air (U.S.Pat. No. 3,108,141). Other prior art appears to be contradictory (U.S.Pat. No. 3,336,403) in teaching the use of peroxides is undesirable dueto polymerization problems, and further that the use of oxygen or airsimultaneously with HBr is slow. Indeed, it has been found thatin someinstances the hydrobromination of alpha-olefins proceeded rapidly whenair and I-IBr were simultaneously added while in other instances, thereaction was unexplicably slow. It was found, however,

lower temperatures, so as to avoid the necessity for higher pressureequipment to maintain the olefins in the liquid phase. A method has nowbeen discovered which involves recycling a small amount (about 5percent) of activated olefins which in some manner serves to reduce thetime required for activation of the remaining 95 weight percent inactiveolefins by abou two-thirds.

In accordance with the invention, the time required to air-blow andactivate an alpha-olefin hydrobromination is reduced by a process whichcomprises adding at least 4 weight percent of a previouslyactivatedalpha-olefin to the substantially pure alphaolefin charge stockto the air-blowing zone. I

The attached FIG. 1 is a simplified flow diagram of the process of thisinvention. I

to FIG. 1,..a substantially pure alpha-olefin enters reactor 10 throughline l2-where'it is contacted under oxygen which enters reactor 10through line 14 to acthat for a substantially pure olefin, that is, anolefin which contains no detectable amount of oxygen containingmaterials of any type, the reaction with I-IBr in the simultaneouspresence of air was uniformly slow, thus substantiating the generalteachings in US. Pat. No. 3,336,403 The simultaneous addition of air andHBr mustoccur at a temperature less than about 50 C., even in thepresence of a free radical promoter, if substantial amounts of secondaryalkyl bromides are to be avoided. Thus, it was not possible to increasethe temperature of the hydrobromination reaction in the simultaneouspresence of air in order to speed up the slow reaction since, in sodoing, substantial amounts of undesirable secondary bromides wouldresult. It is for this reason that the prior art teaches the use of lowtemperature olefin activation such as the use of ultraviolet light, theaddition of extraneous organic peroxides, such as benzoyl peroxide, orthe prior formation of 020- nides.'All of these methods suffer from thedifficulty that they are expensive and not easily controlled.

As described in copending Ser. No. 856,374 entitled Activation ofOlefins for I-Iydrobromination by Air- Blowing and filed on the samedate as this application in the names of Russell G. Hay, Clarence R.Murphy and William R. Walsh and assigned to the same assignee as thisapplication, the above problems were obviated by pre-air-blowing theolefin at a temperature from 60 to 200 C. for a time sufficient toresult in activation of the olefin and thereafter reacting thealphaolefin with anhydrous HBr in the absence of an extraneously addedcatalyst at a temperature less than 50 C. to produce the desired primaryalkyl bromide.

It is necessary to activate the olefin by air-blowing in the liquidphase. This creates problems, especially for the lower carbon numberolefins, such as the butenes and pentenes, as the air-blowingtemperature increases since higher pressure equipment is required tomaintain the olefins in the liquid phase. The higher air-blowingtemperatures are desired, however, since the timerequired to activatethe olefins is inversely proportional to the temperature and the shortercontact times are obviously advantageous.

Methods were therefore sought to decrease the time required forair-blowing the olefins, especially at the tivate the olefin. Theactivated olefin is removed fromv reactor 10 through line 16 and is sentto hydrobromination reactor 20. A portion of the activated olefin inline 16 is removed through line 18 and is recycled and enters line 12together with the substantially pure olefin into reactor 10. The amountof activated olefin recycled through line 18 amounts to at least about 4weight percent of the total charge entering reactor 10. The anhydrousHBr is added to reactor 20 through line 22 and the hydrobrominatedproduct is removed from reactor 20 through line 24 and is sent to arecovery scheme, not shown, for the recovery of the primary alkylbromide. The alpha-olefin charge stock can be any substantially purealpha-olefin having from four to 30 carbon atoms per molecule and ispreferably an alpha-olefin having from four to 10 carbon atoms permolecule. The alpha-olefin can suitably have the formula:

ilt.

limited to:

butene-l; pentene-l; isobutylene; hexenel; 3-methylbutene-1;4-ethylhexene-l; octene-l; dodecene-l; decenel; octadecene-l;tetradecenel; Z-methyll -nonadecene; eicosene-l; tetracosene-l;

2-octyl-I-dodecene; and mixtures thereof.

While any of the above alpha-olefins can be used in the process of thisinvention to insure the production of primary alkyl bromides without theneed of an extranefor atoms per molecule, such as. ethylene, undertelomerization conditions in the presence of a catalyst such as a GroupIIIA metal alkyl such as defined below, for example, aluminum triethyl.Very pure olefins must be used in the telomerization process since theGroup IIIA metal alkyls act as scavengers for any oxygen containingmaterials which might be present and reduce the efficiency of thetelomerization reaction. Thus, the telomerization products which areobtained are substantially unreactive in the hydrobromination reactionas defined above. For example, the alpha-olefins freshly produced by thetelomerization process result in a'yield of less than 50 mole percent,usually less than 10 mole percent, primary alkyl bromide when reactedwith anhydroushydrogen bromide in the absence of an extraneously addedcatalyst at -10 to C. in a time of about 2 hours. Yet another way toobtain the substantially pure alpha-olefins would be, 'of course, to.distill the alpha-olefins in the contact presence of a Group Me-Ra whereMe is any of the Group IIIA metals'defined aboveand wherein at least oneand preferably all-of R R and R are alkyl radicals having between oneand carbon atoms and wherein any one or two of R R and R, can beselected from the group consisting of hydrogen and halogen radicals.Usually the metal alkyl is an aluminumor boron trialkyl such astriisobutylaluminum or'triisobutylboron.

As noted, the substantially pure alpha-olefin prepared as above wasfound to be substantially. inactive for the addition of HBr in theabsence of an extraneously added free radical promoter. The simultaneousaddition of oxygen in the form of air with the I-IBr to thealpha-olefins proved to be a very slow reaction requiring more than 6hours at 28 C. to produce any appreciable amount of product.

It was found that the olefins could be simply and effectively activatedby pretreatment before the HBr addition, the pretreatment consisting ofcontacting the alpha-olefin charge .stock or the gas containing freemolecular oxygen at a temperature from 60 to 200 C. for a timesufficient to activate the alpha-olefins. By an promoter. Minimum timesas short as 1 minute or less activated olefin is meant one which resultsin a yield of at least 85 mole percent primary alkyl bromide whenreacted with anhydrous hydrogen bromide in the .absence of anextraneously added catalyst at l 0 to 0 I tive for the subsequenthydrobromination reaction.

are effective at the higher air-blowing temperatures, whereas minimumtimes on the order of 6 hours are required at the lower air-blowingtemperatures of about 60C.

The subject invention relates to air-blowing a substantially purealpha-olefin as defined above containing at least about 4 weight percentof a previously activated olefin. The purpose of air-blowing in thepresence of a small amount of previously activated olefin is to decreasethe time required forthe air-blowing-operation. One of the advantages ofthe subject invention is that a lower air-blowing temperature can beemployed to achieve activation in the same time which would be requiredat a higher temperature. It is thus possible. to employ a wider range ofairactivation temperatures than was previously believed economicallyfeasible. Using the methods of this invention, a suitable range ofair-blowing temperatures can be from 50 to 200 C., with the preferredactivation temperatures being from 60 to 150C. I

FIG. 2 attached is a plot on a semi-log paper of the time required vs.temperature to obtain anolefin in the Operative Region, which is theregion where an olefin would be active for the hydrobromination reactionwithout the need for an extraneously added free radical catalyst. Thetimes shown on FIG. 2, however, are those required without the use ofthe present invention. Thus, referring to FIG. 2, at C. a minimum of 6hours would be required to activate the alpha-olefin whereas at 170 C."about 1 minute is required. By operating the air activation step inaccordance with the procedure of this invention, namely by air-blowingin the presence of at least about 4 weight percent of previouslyactivated olefin, the total time required to activate the olefin wouldbe reduced. For example, the activation of octene-l by air-blowing at 70C. would require, referring to FIG. 2, about 6 hours of air-blowing timewhereas the octene-l has been found to be ac tivated in a time of only 2hours at 70 C. by air-blowing a mixture of percent substantially pureoctene-l and 5 weight percent previously activated octene-l. Similarly,care must be taken when using the procedure of the present invention notto conduct the air-blowing operation for a time such that the olefinbecomes inac- Hence', the minimum activation time is reduced byabout'two-thirds when air oxidation. occurs in the presence of about5'weight percent active olefin, and the maximum time of air-blowingbefore reaching an inactive state would correspondingly be reduced byabout two-thirds.

The minimum amount of activated olefin to'recycle is critical and mustbe at least about 4 weight percent of the total charge entering theair-blowing reactor. The recycling of active olefins in amounts lessthan about 4 weight percent is ineffective in reducing the time requiredfor activation in the air-blowing step. Larger amounts of activatedolefins can be recycled if desired, but no further beneficial effectsare received. Thus, quite unexpectedly, the use of greater amounts thanabout 4 weight percent of activated olefins does not aid in reducing theair-blowing time still further. 1 As a result, whether 5 or 25 weightpercent of the charge stock to the air-blowing reactor is composed ofpreviously activated olefins, the time required for air-blowing is aboutthe same and is considerably reduced over the case where only asubstantially pureolefin is airblown. Thus, the amount of recycledactivated olefin which can be utilized in the process of this inventioncan vary from about 4 weight percent to 50 weight percent of the chargestock to the air-blowing step and even greater amounts of recycledolefins can be employed if desired. For economic reasons it is obviouslypreferable to employ the minimum amount of recycled activated olefins,and for this reason the preferred amount of recycled olefin is from 4toweight percent.

Activated olefin's having a carbon number different than thesubstantially pure olefin can also suitably be added in the same amountsto decrease the air-blowing time, but these olefins are not preferreddue to complications in the recovery procedure.

The activation of the substantially pure alpha-olefins occurs quitesimply by passage of a gas containing free molecular oxygen through theliquid alpha-olefin at the desired activation temperature. The termsair-blown or air-blowing in this application refer to blowing with a gascontaining free molecular oxygen which may be, but is not necessarily,air. Means should be provided for insuring intimate contacting betweenthe gas containing free molecular oxygen and liquid olefins to beactivated. For example, the gas containing free molecularoxygen can beadded to the liquid olefin through a sparger which breaks up the gasinto very small bubbles. While additional stirring is not required, itcan be employed if desired. The gas containing free molecularoxygen cansuitably be air, pure oxygen or molecular oxygen diluted with an inertgas such as nitrogen. The gas suitably contains from to 100 mole percentfree molecular oxygen-and preferably from 15 to 40 mole percent freemolecular oxygen.

Amounts of oxygen in the activating gas less than about or from whenceit comes is not critical to the process of the subject invention.

The gaseous hydrogen bromide adds to the activated alpha-olefins in ananti-Markownikoff manner. Markownikoff stated in 1870 that if anunsymmetrical olefin is treated with hydrogen halide the addition willoccur at the carbon-carbon double bond and that the hydrogen will attachitself to the carbon atom bearing the greater number of hydrogen atomsand that the halide would attach itself to the carbon atom bearing theleast number of hydrogen atoms. Thus, the normal or Markownikoffaddition would produce a secondary alkyl bromide whereas theanti-Markownikoff addition produces the more desirable abnormal oranti-Markownikoff primary alkyl bromide.

The hydrogen bromide addition reaction occurs rapidly in any reactorproviding for good mass transfer between the gaseous hydrogen bromidephase and the liquid alpha-olefin phase. For example, suitable masstransfer conditions for the addition of the hydrogen bromide to theolefin are obtained by bubbling the hydrogen bromide gas through theliquid activated olefin using, for example, a porous plate gasdistributor to insure small gas bubbles resulting in a large interphasearea. It is also preferred, of course, to provide vigorous agitation ofthe liquid phase to aid in the mass transfer and also to insure themaintenance of the desirable low reaction temperatures to be definedbelow. Under the excellent mass transfer conditions, the reaction isover in a matter of minutes even employing the low reaction temperaturesto be defined below.

A suitable range of reaction temperatures is from 30 to 50 C., with thepreferred reaction temperatures between 10 and 30 C. The use ofincreased reaction temperatures is undesirable as the highertemperatures promote the normal or Markownikoff addition with theconsequent formation of the less desirable, less stable secondary alkylbromides. When the reaction is operated in the defined temperaturerange, rapid completion of the hydrogen bromide addition oc-- curs withthe suppression of the formation of secondary alkyl bromides. Thus,suitable reaction times are between 1 and 240 minutes, and in thepreferred temperature range the reaction times are usually between 3 and120 minutes.

The reaction pressure can suitably be between atmospheric and blOO psigor more. An increase in reaction pressure tends to increase the reactionrate. However, since the reaction rate is already quite fast atatmospheric pressure, the use of increased reaction pressures, whiletechnically feasible, is not preferred for obvious economic reasons.

The hydrobromination reaction product which is composed predominantly ofprimary alkyl bromides and small amounts of secondary alkyl bromides isusually purged of excess hydrogen bromide in any suitable manner. Forexample, air, nitrogen or helium can be passed or bubbled through thereaction product until it, is free of hydrogen bromide. The resultinghydrogen bromide free alkyl bromide reaction product can then,optionally, be neutralized using any suitable basic solution. Forexample, a 5 percent aqueous solution of sodium bicarbonate issatisfactory and produces tions, neutralization is not required nordesired. The

upper-organic phase containing the alkyl bromides can then be separatedand the alkyl bromide recovered in any suitable manner. 7

The-crude alkyl bromide reaction product can also be recovered bypurging with a non-reactive gas as described above and thereafterdissolving the alkyl bromide in about 1 to about 10 times its volume ofa nonreactive solvent for the .alkyl bromide, such as chloroform orpetroleum ether. The solution of the alkyl bromide in the solvent isthen neutralized as before with a weakly basic solution. Alternatively,the unneutralized solution of the alkyl bromide in the nonreactivesolvent can be washed with water until neutral, and this procedure ispreferred in the case of the more labile alkyl bromides. Whichevermethod is chosen to neutralize, the neutralized solution is then driedin any conventional manner, such as by drying over magnesium sulfate.The solvent can then be removed by evaporation or distillation underreduced pressure. The pure alkyl bromide reaction product can then bedistilled from the dried solvent-free organic phase. The inventionwillbe further described with reference to the following experimental work.

Octene-l which was prepared by the telomerization of ethylene, wasdistilled from tri-n-butylaluminum in a' nitrogen atmosphere to producea substantially pure octene-l. The peroxide number of the distilledoctenel was less than 0.1, the limit of ASTM Test 1832.

A series of runs was made wherein the distilled octene-l was air-blownat varying temperatures and for varying times with and without theaddition of weight percent of a previously air-blown and activatedoctene- The results of this series of runs are shown in Table 1 below.

TABLEI Hydrobromination of Octene-l at --C. to 0C.

Hydrob rumination Referring to Table l, air-blowing the octene-l for 2hours at 70C. resulted in only a 24 mole percent yield of primary alkylbromide after a reaction time of 103 minutes. Example 2 shows that 6hours of air-blowing at 70? C. was sufficient to result in a yield ofprimary alkyl bromide of over 90 percent in a reasonable reaction timeof 6 minutes. In this application, yield means the conversion of theolefin times the efficiency of conversion of the olefin to the desiredprimary alkyl bromide. Examples 3 and 4 show that when air-blowingoccurred in .the presence of 5 percent of a previously air-blownactivated octene-l, a time of 2 hours at 70 C. was sufficient to resultin a yield of primary alkyl bromide of over 90 percent in a reactiontime of-3 to 5 minutes. The 5 percent air-blown activated olefin whichwas utilized in Examples 3 and 4 above was part of the product ofExample 2 in Table 1.

EXAMPLE 5.

140 grams of a mixture of hexene-l (95 weight percent) and activatedoctene-l (5 weight percent) was air-blown for 2 hours at 60 C. Theresulting mixture of olefms was found to give a yield of primary alkylbromide of 96 mole percent in a hydrobromination reaction time of 5minutes at-l0 to 0 C.

EXAMPLE 6 140 grams of a mixture of 95 weight percent dodecene-l and 5weight percent of activated octene-l was air-blown for 2 hours at atemperature of C. Hydrobromination of this air-blown mixture of olefinsfor 5 minutes at l0 to 0 C. resulting in an v89 mole percent yield ofprimary alkyl bromides.

EXAMPLE7 EXAMPLE 8 212.6 grams of octene-l were air-blown at atemperature of 70 C. for 2 hours in the presence of 25 weight percent ofpreviously. blown activated octene-l. The resulting mixture of olefinswas active for the hydrobromination reaction which is shown by the factthat more than a 90-mole percent yield of primary alkyl bromide wasobtained at 12 to 0 C. in a time of less than 10 minutes.

A comparison of Example 8 with Example 6 shows that the presence of 25weight percent activated olefin in the charge stock achieved about thesame results as the presence of 5 weight percent activated olefin in thecharge stock. Hence, while it is not detrimental to have larger amountsof activated olefin admixed with the substantially pure olefin, there isno advantage to this process to the presence of the larger quantities ofactivated olefin which merely serve to reduce the space time yield ofproducts from the air-blowing reactor.

EXAMPLE 9 Example 6 was repeated except the amount of activated olefinin the charge stock to the air-blowing step was 2 weight percent. Sixhours were required at 70 C. to activate the mixture.

A comparison of Examples6, 7 and 9 shows that it required as much timewith 2 weight percent activated olefin as with a percent substantiallypure olefin charge stock (Example 6).

A comparison of all of the above examples shows it is critical to employan amount of activated olefin in the charge stock of at least about 4weight percent to obtain the advantages of this invention, i.e., areduction in the minimum time required for activation of the olefin forhydrobromination.

The above data were obtained in a batch type reactor. In a continuousstirred tank reactor where inactive olefin is continuously added andactive olefin is continuously removed, there is considerable backmixingwhich is equivalent to recycle of active olefin, and this type ofrecycle operation is, of course, meant to be included in this invention.

Resort may be had to such variations and modifications as fall withinthe spirit of the invention and the scope of the appended claims.

We claim: a

1. A process for the preparation of a primary alkyl bromide from asubstantially pure alpha-olefin having from four to 30 carbon atoms permolecule which comprises:

contacting at least one of said alpha-olefins in an airblowing zone witha gas containing free molecular to equal at least 4 weight percent ofthe olefins entering said air-blowing zone; and thereafter reacting saidactivated alpha-olefin with anhydrous HBr in the absence of anextraneously added catalyst at a temperature less than 50 C. to producethe desired primary alkyl bromide.

2. A process according to claim 1 wherein said alphaolefin is one whichhas been intimately contacted with a Group IllA metal alkyl having atleast one carbon to metal bond.

3. A process according to claim 2 wherein the gas containing freemolecular oxygen is air.

4. A process according to claim 3 wherein the alphaolefin is octene-l.

5. A process according to claim 1 wherein said previously activatedolefin has a different number of carbon atoms than said substantiallypure alpha-olefin.

6. A process according to claim 5 wherein the substantially pure alphaolefin is hexenel 7. A process according'to claim 5 wherein the substantially pure alpha-olefin is dodecene-l.

8. A method according to claim 1 wherein said alpha-olefins contain from4 to 50 weight percent of a previously activated olefin.

9. A method according to claim 8 wherein said alpha-olefin is obtainedby the telomerization of ethylene under telomerization conditions in thepresence of a Group lIlA metal alkyl.

2. A process according to claim 1 wherein said alphaolefin is one whichhas been intimately contacted with a Group IIIA metal alkyl having atleast one carbon to metal bond.
 3. A process according to claim 2wherein the gas containing free molecular oxygen is air.
 4. A processaccording to claim 3 wherein the alpha-olefin is octene-1.
 5. A processaccording to claim 1 wherein said previously activated olefin has adifferent number of carbon atoms than said substantially purealpha-olefin.
 6. A process according to claim 5 wherein thesubstantially pure alpha-olefin is hexene-1.
 7. A process according toclaim 5 wherein the substantially pure alpha-olefin is dodecene-1.
 8. Amethod according to claim 1 wherein said alpha-olefins contain from 4 to50 weight percent of a previously activated olefin.
 9. A methodaccording to claim 8 wherein said alpha-olefin is obtained by thetelomerization of ethylene under telomerization conditions in thepresence of a Group IIIA metal alkyl.